When you look in the mirror each morning, you see your face: two eyes, a nose, a mouth. But how exactly did the face evolve? Now, scientists have uncovered new fossil evidence that reveals the origin of one of the most significant parts of our anatomy: our face.
Vertebrates, which are animals with backbones, come in two basic models: jawless and jawed. Today, the only jawless vertebrates are lampreys and hagfishes. In the embryos of these jawless vetebrates, blocks of tissue grow forward on either side of the brain, meeting in the midline at the front to create a big upper lip surrounding a single midline "nostril" that lies just in front of the eyes. In jawed vertebrates, in contrast, this same tissue grows forward in the midline under the brain, pushing between the left and right nasal sacs which open separately to the outside. Until now, though, very little has been found about the intermediate steps of this transformation.
Now, though, scientists may have their answer. They studied the skull of Romundina, an early armored fish with jaws, or placoderm, from arctic Canada. By imaging the internal structure of the skull, the researchers found that the skull housed a brain with a short front end, very similar to that of a jawless vertebrate.
"In effect, Romundina has the construction of a jawed vertebrate but the proportions of a jawless one," said Per Ahlberg, one of the researchers, in a news release. "This shows that the organization of the major tissue blocks was the first thing to change, and that the shape of the head caught up afterward."
The findings reveal a little bit more about the evolution of faces and how exactly jawed and jawless vertebrates relate to one another.
The findings are published in the journal Nature.
